On Wed, 10 Nov 2021 10:17:59 -0500 Harry Wentland <harry.wentland@xxxxxxx> wrote: > On 2021-11-10 06:55, Ville Syrjälä wrote: > > On Wed, Nov 10, 2021 at 10:49:24AM +0200, Pekka Paalanen wrote: > >> On Wed, 10 Nov 2021 00:02:16 +0200 > >> Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > >> > >>> On Tue, Nov 09, 2021 at 03:47:58PM -0500, Harry Wentland wrote: > >>>> On 2021-11-08 04:54, Pekka Paalanen wrote: > >>>>> On Thu, 4 Nov 2021 12:27:56 -0400 > >>>>> Harry Wentland <harry.wentland@xxxxxxx> wrote: > >>>>> > >>>>>> On 2021-11-04 04:38, Pekka Paalanen wrote: > >>>>>>> On Wed, 3 Nov 2021 11:08:13 -0400 > >>>>>>> Harry Wentland <harry.wentland@xxxxxxx> wrote: > >>>>>>> > >>>>>>>> On 2021-09-06 17:38, Uma Shankar wrote: > >>>>>>>>> Existing LUT precision structure is having only 16 bit > >>>>>>>>> precision. This is not enough for upcoming enhanced hardwares > >>>>>>>>> and advance usecases like HDR processing. Hence added a new > >>>>>>>>> structure with 32 bit precision values. > >>>>>>>>> > >>>>>>>>> This also defines a new structure to define color lut ranges, > >>>>>>>>> along with related macro definitions and enums. This will help > >>>>>>>>> describe multi segmented lut ranges in the hardware. > >>>>>>>>> > >>>>>>>>> Signed-off-by: Uma Shankar <uma.shankar@xxxxxxxxx> > >>>>>>>>> --- > >>>>>>>>> include/uapi/drm/drm_mode.h | 58 +++++++++++++++++++++++++++++++++++++ > >>>>>>>>> 1 file changed, 58 insertions(+) > >> > >> ... > >> > >>>>>> If the framebuffer is not in FP16 the question then becomes how > >>>>>> the integer pixel values relate to LUT addressing. > >>>>> > >>>>> Traditionally, and in any API I've seen (GL, Vulkan), a usual mapping > >>>>> is to match minimum unsigned integer value to 0.0, and unsigned maximum > >>>>> integer value to 1.0. This is how things work on the cable too, right? > >>>>> (Also taking full vs. limited range video signal into account. And > >>>>> conversion to cable-YUV if that happens.) > >>>>> > >>>>> If you want integer format FB values to map to something else, then you > >>>>> have to tag the FB with that range information, somehow. New UAPI. > >>>>> > >>>> > >>>> On the cable we send integer values, not floating point. AMD HW uses > >>>> floating point internally, though, and the PWL API defines floating > >>>> point entries, so on some level we need to be clear what the floating > >>>> point entries mean. Either we document that to be [0.0, 1.0] or we > >>>> have some UAPI to define it. I'm leaning toward the latter but have > >>>> to think about it some more. > >>> > >>> As for Intel hw if you have an integer pixel value of 0xff... (with > >>> however many bits you have with a specific pixel format) it will get > >>> extended to 0.fff... (to whatever precision the pipe has internally). > >>> So if we go by that a fixed point 1.0 value in the proposed > >>> drm_color_lut_range would be considered just outside the gamut. And > >>> pretty sure fp16 input of 1.0 should also result in a 0.fff... internal > >>> value as well [1]. I think that definition pretty much matches how GL > >>> UNORM<->float conversion works as well. > >> > >> Does it work that way in GL though? > >> > >> I've always thought that with GL_UNSIGNED_BYTE, 0xff maps to 1.0, not > >> 255.0/256.0. ... > > > > That seems to match what I said, or at least tried to say (~0 <-> 1.0 in > > float). drm_color_lut_range being fixed point would follow the ~0 side of > > that. Or at least that interpretation would very easily map to our hw. > > > > If I understand you right Intel HW represents 0xff (assuming 8 bpc) as > the largest (representable) float that is less than 1.0. That float would > be bigger than 255.0/256.0 but smaller than 256.0/256.0. I was just really confused and re-reading what Ville wrote originally now makes sense to me. So, not what Harry wrote. Let me attempt to reiterate and mark fixed point hex values with a h to discriminate from float values. With 8-bit: 0x00 -> 0.000000..0h = 0.0 float 0xff -> 0.ffffff..fh = 1.0 float Then 1.000..0h is the first value out of range. Thanks, pq
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